As is generally known, the surfaces of certain polymers, for example thermoplastic polymers, are inherently non-wettable or hydrophobic. It is also generally known that thermoplastic polymers, for example polyolefin polymers, may be formed into fibers. Such polyolefin fibers may be employed in a variety of commercial applications. For some commercial applications, for example absorbent products, disposable absorbent products and disposable nonwoven absorbent products, the inherent hydrophobic nature of such polymers is a disadvantage. As such, before these inherently hydrophobic polymers may be employed in such absorbent products, the hydrophobic nature of these polymers requires alteration.
One method of altering the hydrophobic nature of such polymers, for example shaped polymers, is sulfonation. As used herein, the term "shaped polymer" or "shaped polymers" means any solid form of a polymer, in contrast to a polymer in gaseous or liquid phase, or in solution. Thus, shaped polymers can be in particulate form, such as powder or granules or chips, a molded article, an extruded shape, fibers, woven or nonwoven fabrics, films, foams or the like. As used herein, the term "sulfonation" means methods of forming a compound containing sulfonic acid, the --SO.sub.2 O.sup.- group. Such methods include, for example, converting organic compounds to sulfonic acids or sulfonates containing the structural group C--SO.sub.2 --O.sup.- or in some cases, N--SO.sub.2 --O.sup.-.
However, in many instances, conventional sulfonation methods require the use and/or storage of materials which pose both health and safety concerns. Examples of such materials include, for example, sulfur trioxide, concentrated sulfuric acid, oleum, and chlorosulfuric acid. Additionally, in many instances, when polymers, such as, for example the surfaces of polyolefin nonwoven weds, are subjected to conventional sulfonation methods, undesirable surface discoloration may occur. For instance, fibers formed from un-dyed polymers, such as polyolefin fibers and desirably, polypropylene fibers, are generally translucent. After being subjected to conventional sulfonation methods, the surface color of such fibers changes such that the fibers appear generally yellow, brown or black in color. As previously mentioned, such polymers may have applications as absorbent articles. As such, in some instances, the discoloring of polymer fibers is generally not desirable, particularly when such polymer fibers are incorporated into personal absorbent articles, such as diapers, feminine pads, or adult incontinence articles.
Therefore, there is a need for improved methods of sulfonation which avoid the disadvantages of conventional sulfonation processes. Such an improved sulfonation method and the products thereof are provided by the present invention and will become more apparent upon further review of this specification.